[compiler-rt] Refactor the interception code on windows.

[asan] Fix unittest Asan-x86_64-inline-Test crashing on Windows64

REAL(memcpy) was used in several places in Asan, while REAL(memmove) was not used.
This CL chooses to patch memcpy() first, solving the crash for unittest.

The crash looks like this:

projects\compiler-rt\lib\asan\tests\default\Asan-x86_64-inline-Test.exe
=================================================================
==22680==ERROR: AddressSanitizer: access-violation on unknown address 0x000000000000 (pc 0x000000000000 bp 0x0029d555f590 sp 0x0029d555f438 T0)
==22680==Hint: pc points to the zero page.

AddressSanitizer can not provide additional info.
 SUMMARY: AddressSanitizer: access-violation (<unknown module>)
==22680==ABORTING

Patch by: Wei Wang
Differential Revision: http://reviews.llvm.org/D22232

llvm-svn: 275098